End point detection for direction milling to induce magnetic anisotropy in a magnetic layer

ABSTRACT

A method for manufacturing a magnetic layer with a magnetic anisotropy. The method includes an endpoint detection process for determining an end point to carefully control the final thickness of the magnetic layer. The method includes depositing a magnetic layer and then depositing a sacrificial layer over the magnetic layer. A low power angled ion milling is then performed until the magnetic layer has been reached. The angled ion milling can be performed at an angle relative to normal and without rotation in order to form an anisotropic surface texture that induces a magnetic anisotropy in the magnetic layer. An indicator layer may be included between the magnetic layer and the sacrificial layer in order to further improve endpoint detection.

This application is a continuation application of commonly assigned U.S.patent application 11/542,086 entitled MAGNETIC RANDOM ACCESS MEMORY(MRAM) HAVING INCREASED REFERENCE LAYERS, filed Oct. 2, 2006, whichitself a Continuation in Part of commonly assigned U.S. patentapplication entitled MAGNETORESITIVE SENSOR HAVING MAGNETIC LAYERS WITHTAILORED MAGNETIC ANISOTROPY INDUCED BY DIRECT ION MILLING, applicationSer. No. 11/304,033 filed Dec. 14, 2005, both of which are herebyincorporated by reference.

FIELD OF THE INVENTION

The present invention relates to magnetoresistive field sensors and moreparticularly to a sensor having magnetic layers with strong magneticanisotropy formed by anisotropic texturing of the layer surface throughion milling.

BACKGROUND OF THE INVENTION

The heart of a computer's long term memory is an assembly that isreferred to as a magnetic disk drive. The magnetic disk drive includes arotating magnetic disk, write and read heads that are suspended by asuspension arm adjacent to a surface of the rotating magnetic disk andan actuator that swings the suspension arm to place the read and writeheads over selected circular tracks on the rotating disk. The read andwrite heads are directly located on a slider that has an air hearingsurface (ABS). The suspension arm biases the slider toward the surfaceof the disk and when the disk rotates, air adjacent to the surface ofthe disk moves along with the disk. The slider flies on this moving airat a very low elevation (fly height) over the surface of the disk. Thisfly height is on the order of nanometers. When the slider rides on theair bearing the write and read heads are employed for writing magnetictransitions to and reading magnetic transitions from the rotating disk.The read and write heads are connected to processing circuitry thatoperates according to a computer program to implement the writing andreading functions.

In a typical design, the write head includes a coil layer embedded infirst, second and third insulation layers (insulation stack), theinsulation stack being sandwiched between first and second pole piecelayers. A gap is formed between the first and second pole piece layersby a gap layer at an air bearing surface (ABS) of the write head and thepole piece layers are connected at a back gap. Current conducted to thecoil layer induces a magnetic flux in the pole pieces which causes amagnetic field to fringe out at a write gap at the ABS for the purposeof writing the aforementioned magnetic impressions in tracks on themoving media, such as in circular tracks on the aforementioned rotatingdisk.

In recent read head designs, a spin valve sensor, also referred to as agiant magnetoresistive (GMR) sensor, has been employed for sensingmagnetic fields from the rotating magnetic disk. This sensor includes anonmagnetic conductive layer, hereinafter referred to as a space layer,sandwiched between first and second ferromagnetic layers, hereinafterreferred to as a pinned layer and a free layer, both of which can bemade up by a plurality of layers. First and second leads are connectedto the spin valve sensor for conducting a sense current therethrough.The magnetization of the pinned layer is pinned substantiallyperpendicular to the air bearing surface (ABS) and is relativelyinsensitive to applied magnetic fields. The magnetic moment of the freelayer is biased substantially parallel to the ABS, but is free to rotatein response to external magnetic fields. In the following substantiallyparallel means closer to parallel than perpendicular where substantiallyperpendicular means closer to perpendicular than parallel. Themagnetization of the pinned layer is typically pinned by exchangecoupling with an antiferromagnetic layer. P For a current in plane (CIP)spin-valve sensor, the thickness of the spacer layer is chosen to beless than the mean free path of conduction electrons through the sensor.With this arrangement, a portion of the conduction electrons isscattered by the interfaces of the spacer layer with each of the pinnedand free layers. When the magnetizations of the pinned and free layersare parallel with respect to one another, scattering is minimal and whenthe magnetizations of the pinned and free layer are antiparallel,scattering is maximized. Changes in scattering alter the resistance ofthe spin valve sensor in proportion to cos θ, where θ is the anglebetween the magnetizations of the pinned and free layers. Since θ isnear 90 degrees at zero field, the resistance of the spin valve sensor(for small rotations of the free layer from 90 degrees) changesproportionally to the magnitudes of the magnetic fields from therotating disk. When a sense current is conducted thorough the spin valvesensor, resistance changes cause potential changes that are detected andprocessed as read-back signals.

When a spin valve sensor employs a single pinned layer it is referred toas a simple spin valve. When a spin valve employs an antiparallel (AP)pinned layer it is referred to as an AP pinned spin valve. An AP pinnedspin valve includes first and second magnetic layers separated by a thinnon-magnetic coupling layer such as Ru or Ir. The thickness of thecoupling layer is chosen so as to antiparallel couple the magneticmoments of the ferromagnetic layers of the pinned layer. A spin valve isalso known as a top or bottom spin valve depending upon whether thepinning layer is at the top (formed after the free layer) or at thebottom (before the free layer).

Magnetization of the pinned layer is usually fixed by exchange couplingone of the ferromagnetic layers (AP1) with a layer of antiferromagneticmaterial such as PtMn. While an antiferromagnetic (AFM) material such asPtMn does not in and of itself have a net magnetic moment, when exchangecoupled with a magnetic material, it can strongly pin the magnetizationof the ferromagnetic layer.

A current in plane (CIP) spin valve sensor is located between first andsecond nonmagnetic electrically insulating read gap layers and the firstand second read gap layers are located between ferromagnetic first andsecond shield layers. In a merged magnetic head a single ferromagneticlayer functions as the second shield layer of the read head and as thefirst pole piece layer of the write head. In a piggyback head the secondshield layer and the first pole piece layer are separate layers.

The ever increasing demand for greater data rate and recording densityhas lead a push tp develop sensors having ever decreasing dimensionssuch as decreased track-width and stripe height. However, as describedabove, in order for a magnetoresistive sensor to operate as desired,various layers such as the free and pinned layers must have theirmagnetic domains oriented in desired directions. For example, the freelayer must remain biased in a direction substantially parallel with theABS, while the pinned layer must have a magnetization that remainspinned in a desired direction substantially perpendicular to the ABS. Assensors become smaller the ability to maintain these magnetic statesdiminishes greatly. Free layers lose biasing, becoming unstable, andpinned layer magnetizations can flip, a situation that leads toamplitude flipping. Both of these situations render the sensor unusable.A technique for (generating a magnetic anisotropy in any desireddirection in the various layers would greatly facilitate sensorrobustness.

In a similar manner, the performance of other components of a magneticrecording system would be greatly improved if a magnetic anisotropycould be generated and could be oriented in any desired direction. Forexample, the performance of a magnetic write element, magnetic shieldsor a magnetic medium could be greatly improved if a technique existedfor orienting a magnetic anisotropy in a desired direction in suchdevices. Likewise, the performance of magnetic memory cells thatincorporate magnetoresistive memory elements can be greatly improved ifa magnetic anisotropy could be generated and could be oriented in anydesired direction.

Therefore, there remains a need for a technique for generating amagnetic anisotropy in a magnetic material layer used in a magneticdevice such as a magnetoresistive sensor, a write element, a magneticshield, a magnetic medium or a magnetic memory cell of a magnetic randomaccess memory (MRAM).

SUMMARY OF THE INVENTION

The present invention provides a method for manufacturing a magneticlayer with a magnetic anisotropy. The method includes an endpointdetection process for determining an end point to carefully control thefinal thickness of the magnetic layer. The method includes depositing amagnetic layer and then depositing a sacrificial layer over the magneticlayer. A low power angled ion milling is then performed until thesacrificial layer is detected indicating that the magnetic layer isabout to be reached.

The angled ion milling can be performed at an angle relative to normaland without rotation in order to form an anisotropic surface texturethat induces a magnetic anisotropy in the magnetic layer. An indicatorlayer may be included between the magnetic layer and the sacrificiallayer in order to further improve endpoint detection.

These and other features and advantages of the invention will beapparent upon reading of the following detailed description of preferredembodiments taken in conjunction with the Figures in which likereference numerals indicate like elements throughout.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and advantages of thisinvention, as well as the preferred mode of use, reference should bemade to the following detailed description read in conjunction with theaccompanying drawings which are not to scale.

FIG. 1 is a schematic illustration of a disk drive system in which theinvention might be embodied;

FIG. 2 is an ABS view of a sensor according to an embodiment of theinvention;

FIG. 3 is an ABS view of a sensor according to another embodiment of theinvention;

FIG. 4 is an ABS view of a sensor according to another embodiment of theinvention;

FIGS. 5A through 5D are cross sectional views illustrating a method ofsetting a magnetic anisotropy in a magnetic layer according to thepresent invention; and

FIG. 6 is a schematic illustration describing an ion milling endpointdetection method according to an embodiment of the invention;

FIG. 7 is a schematic illustration describing an ion milling endpointdetection method according to another embodiment of the invention;

FIG. 8 is a cross sectional view of a magnetic write bead according toan embodiment of the invention;

FIG. 9 is an ABS view, taken from line 9-9 of FIG. 8, of the magneticwrite head of FIG. 8;

FIGS. 10-14 are views of a magnetic write head in various intermediatestages of manufacture, illustrating a method of constructing a magneticwrite pole according to an embodiment of the invention;

FIG. 15 is a partial, cross sectional view of a magnetic medium (disk)according to an embodiment of the invention;

FIG. 16 is a perspective view of a magnetic medium (disk) according toan embodiment of the invention;

FIGS. 17-20 are perspective views illustrating a method of constructinga magnetic medium (disk) according to embodiments of the invention;

FIG. 21 is an ABS view of a magnetic read head according to anembodiment of the invention;

FIGS. 22-26 are views illustrating methods of constructing magneticshields according to various embodiments of the invention; and

FIG. 27 is a graphical representation illustrating a relationshipbetween etching time and magnetic anisotropy;

FIG. 28 is a graphical representation illustrating a magnetic anisotropyprovided by the present invention;

FIG. 29 is a graphical illustration of a relationship between thicknessand anisotropy;

FIG. 30 is a perspective schematic view of a Magnetic Random AccessMemory (MRAM) array, and

FIG. 31 is a side, cross sectional view of a magnetic memory cell of aMagnetic Random Access Memory (MRAM) array.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description is of the best embodiments presentlycontemplated for carrying out this invention. This description is madefor the purpose of illustrating the general principles of this inventionand is not meant to limit the inventive concepts claimed herein.

Referring now to FIG. 1, there is shown a disk drive 100 embodying thisinvention. As shown in FIG. 1, at least one rotatable magnetic disk 112is supported on a spindle 114 and rotated by a disk drive motor 118. Themagnetic recording on each disk is in the form of annular patterns ofconcentric data tracks (not shown) on the magnetic disk 112.

At least one slider 113 is positioned near the magnetic disk 112, eachslider 113 supporting one or more magnetic bead assemblies 121. As themagnetic disk rotates, slider 113 moves radially in and out over thedisk surface 122 so that the magnetic head assembly 121 may accessdifferent tracks of the magnetic disk where desired data are written.Each slider 113 is attached to an actuator arm 119 by way of asuspension 115. The suspension 115 provides a slight spring force whichbiases slider 113 against the disk surface 122. Each actuator arm 119 isattached to an actuator means 127. The actuator means 127 as shown inFIG. 1 may be a voice coil motor (VCM). The VCM comprises a coil movablewithin a fixed magnetic field, the direction and speed of the coilmovements being controlled by the motor current signals supplied bycontroller 129.

During operation of the disk storage system, the rotation of themagnetic disk 112 generates an air bearing between the slider 113 andthe disk surface 122 which exerts an upward force or lift on the slider.The air bearing thus counter-balances the slight spring force ofsuspension 115 and supports slider 113 off and slightly above the disksurface by a small, substantially constant spacing during normaloperation.

The various components of the disk storage system are controlled inoperation by control signals generated by control unit 129, such asaccess control signals and internal clock signals. Typically the controlunit 129 comprises logic control circuits, storage means and amicroprocessor. The control unit 129 generates control signals tocontrol various system operations such as drive motor control signals online 123 and head position and seek control signals on line 128. Thecontrol signals on line 128 provide the desired current profiles tooptimally move and position slider 113 to the desired data track on disk112. Write and read signals are communicated to and from write and readheads 121 by way of recording channel 125.

Magnetoresistive Sensor Having Magnetic Layers With Tailored AnisotropyInduced By Direct Ion Milling

With reference now to FIG. 2, a magnetoresistive sensor 200 according tothe present invention is described. The sensor 200 includes a sensorstack 202 sandwiched between first and second non-magnetic, electricallyinsulating gap layers 204, 206. The first and second hard bias layers208, 210 extend laterally from the sides of the sensor stack 202. Thehard bias layers may be deposited over seed layers 212, 214. First andsecond leads 216, 218 are deposited over the hard bias layers 208, 210,and may be constructed of for example Au, Rh or some other electricallyconductive material.

With continued reference to FIG. 2, the sensor stack 202 includes amagnetic free layer 220, a magnetic pinned layer structure 222 and aspace layer 224 sandwiched between the free and pinned layers 220, 222.The free layer 220 has a magnetic moment 221 that is biased in adirection substantially parallel with the ABS, but that is free torotate in response to a magnetic field. The pinned layer 222 may be ofvarious configurations, such as simple, AP coupled,, AFM pinned or selfpinned. The free layer 220 can be constructed of one or more layers offor example NiFe, Co, CoFe or other sufficiently soft magnetic material,preferably with a layer of Co or CoFe adjacent to the spacer layer 224.The spacer layer 224 can be constructed of a non-magnetic, electricallyconductive material such as Cu.

The pinned layer 222 is preferably an AP coupled pinned layer havingfirst and second magnetic layers AP1 226 and AP2 228 which areantiparallel coupled across an AP coupling layer 230. The AP1 and AP2layers can be for example CoFe or some other suitable magnetic material.The coupling layer 230 can be constructed of, for example, Ru or Ir andis constructed of a thickness chosen to strongly antiparallel couple themagnetic moments 234 and 236 of the AP1 and AP2 layers, respectively.The coupling layer can be for example 2-10 Angstroms thick or about 8Angstroms thick. The AP1 layer 226 may be exchange coupled with a layerof antiferromagnetic material (AFM layer 232) which strongly pins themagnetic moment 234 of the AP1 layer 226 in a desired directionsubstantially perpendicular to the ABS and due to AP coupling of the AP1and AP2 layers 226 and 228 pins the moment 236 of the AP2 layer 228 in adesired direction substantially perpendicular to the ABS, butantiparallel with the moment 234 of the AP1 layer 226.

A seed layer 238 may be provided at the bottom of the sensor stack 202to promote a desired grain structure on the subsequently depositedsensor layers, In addition, a capping layer 240, such as Ta, may beprovided to protect the layers of the sensor stack 202 from damageduring manufacture.

With reference still to FIG. 2, the hard magnetic bias layers 208, 210may be constructed of a magnetic material having a high coercivity of1.5 kOe or higher, preferably Co_(1−x)Pt_(x) or Co_(1−x−y)Pt_(x)Cr_(y)(x being, between 10 and 35 atomic % and y between 0 and 15 atomic %).The seed layers 212, 214 may be constructed of for example, Cr or CrX(X=Mo,Ti,V) on which the magnetic Co_(1−x)Pt_(x) orCo_(1−x−y)Pt_(x)Cr_(y) material is deposited to achieve crystallinetexture and sufficiently high coercivity. The magnetic hard bias layershave magnetic moments that are set substantially parallel to the ABS inorder to bias the moment 221 of the free layer in a desired directionsubstantially parallel with the ABS.

The free layer 220 has a surface 223 that has been treated to have ananisotropic roughness. The treatment and resulting anisotropic roughnessare described below with reference to FIGS. 5A-5D. The treatment of thesurface 223 (described in greater detail below) of the free layer 220 isperformed at such an angle that the anisotropic roughness will beoriented in such a manner to cause the free layer to have a magneticanisotropy 225 oriented substantially parallel with the air bearingsurface (ABS) as desired. Here and in the following the magneticanisotropy axis shall refer to the magnetic easy axis. In the presentcase this means that the magnetic easy axis will be orientedsubstantially parallel to the ABS. The magnetic anisotropy 225 of thefree layer greatly assists the biasing robustness of the free layer 220,and is completely additive to the biasing provided by the hard biaslayers 208, 210.

With reference still to FIG. 2, one or both of the AP1 and AP2 layers226, 228 can have surfaces 227, 229 that are treated with an anisotropicroughness that induces a magnetic anisotropy 231, 233 substantiallyperpendicular to the ABS as desired. This surface treatment is performedat such an angle that the anisotropic roughness will be oriented in sucha manner to cause the magnetic anisotropy 231, 333 to be oriented in adirection substantially perpendicular to the ABS as desired.

It should be pointed out that either or both of the free and pinnedlayers 220, 222 can be treated as described to have an anisotropicroughness. If both the free layer and pinned layers 220, 222 are treatedas described, the present invention advantageously allows theanisotropies of the free layer 225 and pinned layer 231, 233 to be setin different direction as necessary.

It should also be pointed out that the strength of the magneticanisotropy 225, 231, 233 after removing a given amount of material isinversely proportional to the remaining thickness of the layer beingtreated. Therefore, if a stronger magnetic anisotropy is needed,multiple treated layers may be deposited. For example, if the free layer220 is too thick to have a sufficiently strong anisotropy 225, a firstlayer may be deposited, then treated as described, then a second layercan be deposited and treated. The number of layers can be increased (andtheir individual thickness decreased) as needed to achieve asufficiently strong anisotropy.

With reference now to FIG. 3, a sensor 300 according to anotherembodiment of the invention includes a sensor stack 202, sandwichedbetween first and second gap layers 204, 206. As with the previouslydescribed embodiment, the sensor 300 includes a free layer 220, a pinnedlayer 222 and a non-magnetic spacer layer 230. Also, as with thepreviously described embodiments, the free layer 220 has a surface 223that is configured with an anisotropic surface texture that induces astrong magnetic anisotropy 225 in the free layer in a directionsubstantially parallel with the ABS. One or more of the magnetic layers226 228 of the pinned layer may also have a surface configured with ananisotropic texture 227, 229 that induces a strong magnetic anisotropy231, 233 in a direction substantially perpendicular to the ABS. Themagnetic moment of the free layer 220 is maintained in a biased stateparallel with the ABS by the strong magnetic anisotropy 225 provided bythe surface texture 223. Because the free layer is biased by itsmagnetic anisotropy, 225, the bias layers 208, 210 provided in thepreviously described embodiment (FIG. 2) are not needed in theembodiment described here in FIG. 3. Therefore, the areas outside of thesensor stack 202, between the first and second gap layers 204, 206 maybe filled with a non-magnetic, electrically conductive lead material304, 306, such as Au, Rh, Cu or some other suitable material.Alternatively, the areas outside of the sensor stack 202 (ie. extending,laterally beyond the sides of the sensor stack 202) may include acombination of fill material such as alumina and an electricallyconductive lead material.

With reference to FIG. 4, another embodiment of the invention includes acurrent perpendicular to plane (CPP) sensor 400 that includes a sensorstack 402 having a free layer 220, a pinned layer structure 222, and anon-magnetic layer 404 sandwiched between the free layer 220 and thepinned layer structure 222. The sensor 400 can be a tunnel valve or acurrent perpendicular to plane giant magnetoresistive sensor (CPP GMR).If the sensor 400 is a tunnel valve, the non-magnetic layer 404 is athin, non-magnetic, electrically insulating barrier layer 404, such asalumina (Al₂O₃) or MgO. If the sensor 400 is a CIP GMR sensor, then thenon-magnetic layer 404 is an electrically conductive spacer layer, suchas Cu.

The sensor stack 402 is sandwiched between first and second electricallyconductive leads 406, 408, which may be constructed of a magneticmaterial such as NiFe so that they may function as magnetic shields aswell as leads. The free layer 220 has a surface 223 configured with ananisotropic texture that induces a magnetic anisotropy 225 substantiallyparallel with the free layer. First and second hard magnetic bias layers410, 412 may be provided at either side of the sensor stack 402 to biasthe moment 221 of the free layer 220. The bias layers 410, 412, may beconstructed of a material such as CoPt or CoPtCr, and are insulated fromthe sensor stack 402 and at least one of the shields/leads 406 byinstallation layers 414, 416, which may be constructed of, for example,alumina and which may be conformally deposited by a technique such aschemical vapor deposition (CVD) or atomic layer deposition (ALD). Theinsulation layers 414, 416 prevent current from being shunted throughthe hard bias layers 410, 412. Optionally, the hard bias layers 410, 412can be omitted, and biasing of the moment 221 of the free layer 220 canbe maintained solely by the magnetic anisotropy 225 provided by thesurface texture 223.

It should be pointed out that, although the pinned layers structure 222,described with reference to FIGS. 2, 3 and 4 is described as beingpinned by exchange coupling with an AFM layer 232, this AFM layer 232could be eliminated from any one of these embodiments. In that casepinning of the moments 234, 236 of the pinned layer structure 222 can bemaintained by a combination of AP coupling between the AP1 and AP2layers 226, 228, positive magnetostriction of the AP1 and AP2 layers226, 228, and the magnetic anisotropy 231, 233 provided by anisotropictexture of the surfaces 227, 229.

The free layer 220 described with reference to FIGS. 2, 3 and 4 can beconstructed of, for example Co, CoFe, NiFe or a combination of thesematerials. The AP1 and AP2 layers 226, 228 of the pinned layer structure222 described with reference to FIGS. 2, 3, and 4 can be constructed of,for example CoFe or some other suitable material. It should be pointedout that the use of surface treated magnetic layers in amagnetoresistive device applies to any magnetic layer of any type ofmagnetoresistive sensor, memory cell, or magnetic device of anystructure, including current in plane (CIP), current perpendicular toplane tunnel valves (CPP TMR), current perpendicular to plane giantmagnetoresistive sensor (CPP GMR), dual sensors, spin-accumulationsensors, magnetic transistors, MRAM, etc.

As described above, in a free layer the surface texture induced magneticanisotropy can be used in place of hard bias layers or can be used inconjunction with such hard bias layers. In addition, the surface textureenhanced magnetic anisotropy can be used in conjunction with andadditive to any other biasing structure, such as in-stack bias or directorthogonal exchange biasing.

In addition, the anisotropic texture induced magnetic anisotropy in afree layer can be practiced in a sensor having an AP coupled free layer,also known as a synthetic free layer. Such a structure includes two ormore magnetic layers separated by and antiparallel-coupled across anon-magnetic coupling layer, which can be, for example Ru. The magneticlayers can each be treated as described, or alternatively, less thanall, for example, one of the magnetic layers can be treated asdescribed.

Anisotropic Texturing of a Magnetic Layer for Inducing a MagneticAnisotropy in the Magnetic Layer

With reference to FIGS. 5A through 5D a magnetic material 502 isdeposited over a substrate 503. The magnetic layer can be for example afree layer 220 (FIG. 2, 3 or 4) an AP1 or AP2 layer 226, 228 (FIG. 2, 3or 4) or some other magnetic layer in a magnetoresistive sensor, amagnetic write head, a magnetic medium a magnetic electrode of amagnetic random access memory (MRAM) cell, or some other devices. Themagnetic material 502 can be for example 30 to 300 Angstroms or about100 (Angstroms thick after ion beam milling. An ion milling (or etch) isthen performed by directing an ion beam 504 at an angle θ with respectto a normal to the surface of the magnetic layer 502. The angled ionmilling (or etch) induces an anisotropic roughness or texture forexample in the form of oriented ripples or facets 506 that run in adirection substantially parallel or substantially perpendicular to thein-plane projection 507 of the ion beam 504 onto the surface of thelayer 502. The typical or average pitch P of the ripples 506 may bebetween 10-200 nm, and their average depth D may be between 0.5 to 5 nmor about 1 nm.

A magnetic easy axis 501 of the magnetic layer 502 will be generated bythe anisotropic texture. Depending, on the material composition andother factors such as the ion beam energy and substrate temperature, themagnetic easy axis may be either perpendicular or parallel to thedirection 512 of the ripples and substantially perpendicular or parallelto the in-plane projection 506 (FIG. 5B) of the angled ion milling ontothe surface of the under layer 502. Therefore, the ion milling directionmust be chosen such that the resulting magnetic easy axis of themagnetic layers is in the proper, desired direction (such assubstantially parallel with the ABS for a free layer or in-stack biaslayer or substantially perpendicular to the ABS for a pinned layer.

The angled ion beam 504 is preferably oriented at an angle of between 20and 80 degrees and is more preferably oriented at an angle of between 5and 65 degrees with respect to the normal to the surface of theunderlayer 502. The exact voltage, current, and angle conditions dependon the type and characteristics of the ion source in use. Typically alow energy ion beam energy such as 80 to 120 eV or about 100 eV isemployed.

The initial thickness of the layer 502 and the milling time and strengthare chosen to result in a final magnetic layer 502 having a desiredfinal thickness.

End Point Detection For Direct Ion Milling to Induce Magnetic Anisotropy

In order to optimize the effectiveness of the direct ion milling methoddescribed above, it is important to carefully control the resultingfinal thickness after the ion milling has been completed. The finalthickness of the magnetic layer will not only affect the efficiency ofthe resulting magnetic anisotropy, but will also affect the performanceof the magnetic layer for its intended function. For example, thethickness of a free layer is very important to the performance of thefree layer. As can be appreciated, the direct ion milling removesmaterial from the magnetic layer, and the longer the ion milling and thestronger the power, the greater the amount of the material removed.

With reference to FIG. 6, a novel endpoint detection method is describedfor determining at what point the ion milling should terminate in orderto produce a magnetic layer having a desired final thickness. Themagnetic film can be deposited substantially to its desired finalthickness, or possibly slightly thicker. A magnetic layer 602 isdeposited onto a substrate 604, which can be any form of under-layer. Asacrificial film 606 is deposited over the magnetic layer 602. Thissacrificial film 606 is preferably constructed of a different materialthan the magnetic layer 602.

A stationary angled ion beam 608 performs an ion milling, using an ionsource 610 in order to remove sufficient sacrificial layer material tocreate an anisotropic roughness on its surface. An etch detector 612,such as SIMS (Secondary Ion NMass Spectrometer) detects material removedby the ion beam 608. As the sacrificial layer 606 is being removed bythe ion beam 608, the etch detector will detect sacrificial layerparticles. When the ion beam 608 has sufficiently removed thesacrificial layer 606 (ie. the magnetic layer 602 has been reached),then the etch detector 612 will begin to detect particles of materialmaking up the magnetic layer 602. This indicates that ion milling can beterminated. The sacrificial layer 606 material is chosen experimentallyto create the most favorable anisotropic roughness by ion milling. Anyanisotropic roughness from the sacrificial layer 606, will betransferred into the magnetic layer 602.

With reference to FIG. 7, in an alternate embodiment of the invention, amagnetic layer 702 is deposited on a substrate 704, the substrate can beany layer such as a spacer layer, a pinned layer seed layer, a Ru APcoupling layer, or any other layer that might be present under amagnetic layer that would benefit from the described surface treatment.A thin indicator layer 706 is deposited on the magnetic layer 702, and asacrificial layer 708 may be deposited on the indicator layer. Astationary ion beam 710 is provided by an ion source 712, and an etchdetector 714 is provided for detecting the material being removed by theion beam 710 at any give time.

The role of the indicator layer 706 is to indicate when ion millingneeds to be stopped. The detection of the indicator layer 706 can beachieved for example by using SIMS or another in-situ detectiontechnique. If a sufficiently slow etching indicator material incomparison with the sacrificial or magnetic layer material is chosen,then the indicator layer 706 can also act as a milling stop to improvemilling uniformity. The materials of the sacrificial layer 708 andindicator layer 706 are chosen experimentally to create the mostfavorable anisotropic roughness by ion milling. This anisotropicroughness is then transferred into the magnetic layer for maximumanisotropy. The sacrificial material 708 does not remain in the finalsensor. The indicator material 706 may or may not remain in the finalsensor as needed. The indicator layer 706 may be used to simply indicatethe endpoint of the process, or may be used to indicate the point atwhich different milling parameters are needed to finish the process.

For example, the magnetic layer 702 may be Ni, Fe, Co or their alloys,the indicator layer 706 may be one of Ta, Ru, Pt, Cr, Pd, Ti, Al, thesacrificial layer 708 may be one of Ru, Ta, Au, Cu, Ag. The magneticfilm may be a magnetic layer in a magnetic sensor or other magneticdevice in which a uniaxial magnetic anisotropy can improve theperformance of the device. The direction of the ion milling with respectto the substrate is chosen to create the appropriate anisotropicroughness which induces a magnetic anisotropy axis in layer 702 that issubstantially parallel to the ABS is the case of a magnetic free layeror in-stack bias layer or substantially perpendicular to the ABS in caseof a magnetic pinned layer.

Magnetic Write Head With Magnetically Anisotropic Write Pole

With reference now to FIG. 8, the present invention can also be embodiedin a magnetic write head such as a perpendicular magnetic write head800. The write head 800 includes a write pole 802, and a return pole804. The write pole 802 is connected with a magnetic shaping layer 806,and the shaping layer 806 and return pole 804 are connected by amagnetic back gap layer 808. The return pole 804, back gap 808 andshaping layer 806 can be constructed of various magnetic materials suchas NiFe or some other suitable magnetic material. The write pole 802 canbe constructed of various magnetic materials and is preferablyconstructed of a material having a low coercivity and a high moment,such as CoFe. The write pole may also be constructed as a laminatestructure, with many layers of magnetic material separated from oneanother by thin non-magnetic layers.

An electrically conductive coil 810 passes between the return pole 804and the shaping layer 806 and write pole 802. The electricallyconductive coil can be constructed of, for example Cu and is surroundedby an insulation layer 812, which can be one or more layers of, forexample, alumina. The write head 802 may be sandwiched betweenelectrically insulating, non-magnetic layers 814. The write head 800 hasa surface for facing a magnetic medium, also referred to as an airbearing surface or ABS.

With reference still to FIG. 8, as electrical current flows through thecoil 810 (FIG. 9) a magnetic field is induced that results in a magneticflux flowing through the write pole 802, shaping layer 806, back gap 808and return pole 804. This flux makes a complete circuit by emitting awrite field 816 that extends from the write pole 802 and passes throughan adjacent magnetic medium 817 and back to the return pole 804. In atypical perpendicular recording design the magnetic medium 817 has athin high coercivity top layer 819 and a lower coercivity underlayer821. With reference to FIG. 9, which shows the write head as viewed fromthe ABS, the write pole 802 has a much smaller cross section than thereturn pole 804. This means that the magnetic field emitting from thereturn pole 802 is much more concentrated than the magnetic fieldreturning to the return pole 804, because the field at the return pole804 is much more spread out. Therefore, the magnetic field from thewrite pole is sufficiently strong to magnetize the thin, high coercivitytop layer, but is sufficiently weak at the return pole, that it does noterase the signal written by the write pole. It can also be seen withreference to FIG. 9 that the write pole 802 can be constructed with atrapezoidal shape. This shape is helpful in avoiding adjacent trackwriting when the magnetic head is skewed at an angle when the head is atextreme outer or inner radii of a magnetic disk including the magnetic,medium during use.

With continued reference to FIG. 9, the write pole 802 has a laterallyoriented magnetic anisotropy or magnetic easy axis 818 that is orientedperpendicular to a track direction 820 and parallel with the ABS andsurface of a magnetic medium during use (magnetic medium not shown). Asthose skilled in the art will appreciate, during use, the magnetizationof the write head oscillates between positions into and out of the ABS,or into and out of the plane of the page in FIG. 9. Having a magneticeasy axis that is parallel with the ABS (parallel with the plane of thepage in FIG. 9) increases the speed at which the magnetization of thewrite head can oscillate to positions into and out of the ABS.Therefore, this magnetic easy axis 818 greatly increases writing speedand efficiency.

Perhaps more importantly, the magnetic easy axis 818 prevents the writepole 802 from inadvertently writing to a magnetic medium which wouldcause unacceptable signal noise and loss of data. As can be seen withreference to FIGS. 8 and 9, the write pole has a long narrow shape. Thiscauses a shape induced magnetic anisotropy in an undesired directionperpendicular to the ABS. Were it not for the intentionally createdmagnetic anisotropy 818 parallel with the ABS, this shape inducedanisotropy perpendicular to the ABS would cause the write pole 802 to bemagnetized either into or out of the ABS in a quiescent state (ie. whenno current flows through coil 810). As can be appreciated then, theshape induced magnetic anisotropy can cause the write pole 802 to writea signal to a magnetic medium even when such signal is not desired. Thepresence of the intentionally generated magnetic anisotropy 818 preventsthis inadvertent writing by maintaining the magnetization of the writepole 802 in a neutral state when current is not flowing through thecoil. Methods for constructing a write pole 802 to have such a magneticanisotropy 818 according to embodiments of the invention are describedherein below.

With reference to FIGS. 10 through 14, methods for constructing amagnetic write pole having a magnetic anisotropy in a desired directionare described. With particular reference to FIG. 10, a substrate 1002 isprovided, which may be, for example, the insulation layer 812 andshaping layer 806 described in FIGS. 8 and 9, both of which have beenplanarized to have smooth flat coplanar surfaces. An electricallyconductive seed layer 1004 is deposited over the substrate 1002. Theseed layer has a surface 1006 and can be constructed of a magneticmaterial similar to the write pole material or could be a non-magneticelectrically conductive material.

With continued reference to FIG. 10, an angled direct ion beam 1008performs an angled ion milling to form an anisotropic roughness in thesurface 1006 of the seed layer 1004. The ion milling and resultinganisotropic roughness are described in greater detail with reference toFIGS. 5A through 5D.

With reference to FIG. 11, a layer of magnetic material 1010 isdeposited over the seed layer 1004. The magnetic material 1010 can be,for example CoFe or some other magnetic material. A thin layer of hardmask material 1012 is then deposited over the magnetic layer 1010. Thehard mask layer 1012 can be, for example alumina (Al₂O₃), SiO₂, diamondlike carbon (DLC) etc. An image transfer layer 1014, such as DURMIMIDE®can be deposited over the hard mask 1014. A photosensitive mask layer1016, such as photoresist is then deposited over the image transferlayer 1014 and is phlotolithographically patterned to have a width thatis chosen to define a track width of the write pole 802 (FIGS. 8 and 9).

The anisotropic texture of the surface 1006 of the seed layer 1004results in a magnetic easy axis 1018 in the magnetic pole material layer1010. This magnetic anisotropy is described in greater detail in FIGS.5A through 5D. As described above, the effect of the anisotropicroughness in generating a magnetic anisotropy that is (after removing agiven amount of material) inversely proportional to the remainingthickness of the layer being treated. Therefore, if a greater magneticanisotropy 1018 is needed, the magnetic layer 1010 can be deposited inseveral stages by depositing a portion of the magnetic layer 1010,performing an angled ion milling, depositing some more magnetic layer1010, performing another angled ion milling, etc. With each ion millingpreferably being a low powered ion milling as described in FIGS. 5Athrough 5D. The series of angled ion millings can greatly increase theamount of magnetic anisotropy in the write pole 802.

With reference now to FIG. 12, a reactive ion beam 1202 performs areactive ion etch (RIE) to transfer the image of the photoresist mask1016 into the underlying image transfer layer 1014 and the hard masklayer 1012 by removing material not protected by the photo mask 1016.Then, with reference to FIG. 13, an ion beam 1302 performs an ionmilling to remove portions of the magnetic layer 1010 that are notprotected by the hard mask 1012, thereby forming the write pole 802described in FIGS. 8 and 9. The ion milling is preferably performed fromtwo sides at an angle with respect to normal in order to create a writepole having the desired trapezoidal shape discussed with reference toFIG. 9. During ion milling, the ion beam 1302 removes the photoresistlayer 1016 (FIG. 12) and also likely removes a portion of the imagetransfer layer 1014. After the write pole 802 has been formed, aninsulation material can be deposited and the remaining mask layers 1012,1014 can be removed.

With reference now to FIG. 14, in another similar embodiment of theinvention, a multi-layer, laminated write pole can be formed. Asubstrate 1402 is provided and an electrically conductive seed layer1404 is deposited over the substrate 1402. Then a series of alternatingmagnetic layers 1406, and thin, non-magnetic layers 1408 are deposited.The magnetic layers can be constructed of, for example, CoFe and thethin, non-magnetic layers can be constructed of, for example Cr, NiCr,Rh, Ru, Ta, or alumina (Al₂O₃). The magnetic layers 1406 can each have athickness of, for example 100-500 Å, and the non-magnetic layers 1408can each have a thickness of, for example 5-30 Å. Constructing themagnetic pole material as a laminated structure of magnetic layers 1406separated by thin non-magnetic layers 1408 prevents the formation ofmagnetic domains and significantly improves magnetic performance.

After depositing a magnetic layer 1406, the surface of the magneticlayer 1406 is treated with a low-power angled ion beam 1410 in an angledion milling to create a desired anisotropic surface texture as describedin FIGS. 5A through 5D. The surface texture generated by the ion millingis constructed so as to induce a magnetic anisotropy 1412 in a desireddirection substantially perpendicular to the down track direction andsubstantially parallel with the ABS.

It should be pointed out that the final deposited alternating layers ofmagnetic material 1406 and non-magnetic material 1408 will include manysuch layers. It should also be pointed out that the surfaces of anynumber of the magnetic layers 1406 can be treated. For example, only oneor a few of the magnetic layers can be treated by the ion beam 1410during ion milling, or all of the magnetic layers 1406 can be treateddepending upon the strength of the magnetic anisotropy needed.Alternatively, or in addition to treating the surfaces of the magneticlayers 1406, the surfaces of the non-magnetic layers 1408 can be treatedwith the ion beam 1410 during ion milling to produce an anisotropicsurface texture on the non-magnetic layers 1408. The treatednon-magnetic layers, then, become underlayers for the subsequentlydeposited magnetic layers, and this treatment of the underlyingnon-magnetic layers 1408 induces a desired magnetic anisotropy in themagnetic layers 1406 deposited thereon.

Magnetic Medium Having a Soft Underlayer With a Magnetic Anisotropy

With reference now to FIG. 15, a magnetic medium for use inperpendicular magnetic recording includes a substrate 1502, a magneticsoft underlayer 1504 formed on the substrate and a thin magneticallyhard top layer 1506 formed on the underlayer 1504. The substrate may beconstructed of a material such as glass or AlTiC. The magnetically softunderlayer 1504 can be constructed of a relatively low coercivitymaterial such as NiFe₁₄ or CoNb₈Zr₅. The higher coercivity top layer1506 can be constructed of, for example, CoCrPtB. It may be a singlelayer or a multilayer such as antiferromagnetic coupled media.

With reference now to FIG. 16, a magnetic disk 1602 of the magneticmedium is shown with the high coercivity top layer removed for clarityto show the soft underlayer 1504 deposited over the substrate 1502. Thedisk 1602 has a magnetic anisotropy 1604 in the soft underlayer 1504(FIG. 15) that is oriented in a radial direction over substantially theentire area of the disk 1602. Such a radially oriented magneticanisotropy 1604 prevents uncontrolled domain structures from forming inthe soft underlayer 1504, which would otherwise cause unwanted noise andperformance issues. The magnetic anisotropy 1604 tends to keep theunderlayer 1504 magnetized in a direction substantially perpendicular tothe track direction when the disk is not being written to. Furthermore,this magnetic anisotropy is achieved without increasing the magneticcoercivity of the underlayer so that it is still permeable as desired.

With reference to FIG. 17, a method for making a magnetic disk 1602(magnetic medium) with a radially oriented magnetic anisotropy isdescribed. In one possible method of constructing, such a magneticmedium, a substrate 1502 is provided and a magnetically soft underlayer1504 is deposited onto the substrate 1502. After deposition of the softunderlayer 1504, a stationary low powered angled ion beam 1702 performsan angled ion milling to etch the surface 1708 of the soft underlayer atan angle 1704 of, for example 45 degrees, with respect to normal 1710 ofthe surface 1708 of the underlayer 1504. This ion milling and theresulting texture can be better understood with reference to FIGS.5A-5D. The initial thickness of the soft underlayer 1504 is chosen tocreate a desired final thickness of the soft underlayer 1504 after ionmilling with an appropriate anisotropy. For a given final targetthickness, larger anisotropy is obtained with larger initial thicknessand longer milling time.

With continued reference to FIG. 17, in order to form a surface texturethat will induce a radially oriented magnetic anisotropy the ion beam1702 must be angled such that its projection onto the plane of thesurface of the soft underlayer 1504 is either oriented radially ortangentially (circumferentially) while spinning the disk. Depending onthe material composition of the soft underlayer 1504 and other factorssuch as the ion beam energy or the substrate temperature, the magneticanisotropy may be either perpendicular to the ion milling orientation orparallel to the ion milling orientation. For example, with reference toFIG. 17, the projection 1712 of the ion beam 1702 onto the plane of thesurface 1708 is oriented radially with respect to the disk 1602.

With reference to FIG. 18, the ion beam 1702 performs a angled ionmilling such that the projection 1802 of the ion beam 1702 onto thesurface 1708 is oriented along a tangent 1804 of a circle 1806 that isconcentric with the disk. In other words, the ion milling is performedin a circumferential manner. As mentioned above, the choice of whetherto performing the ion milling in a radial direction (as in FIG. 17) orin a circumferential direction (as in FIG. 18) depends on the materialused for the underlayer 1504 and may depend upon other parameters aswell. The goal, howsoever, is to produce an anisotropic texture on thesurface 1708 that will produce a radially oriented magnetic anisotropy1604 (FIG. 16) in the soft underlayer 1504.

With reference to FIG. 19, in order to milling the soft underlayer 1504radially as described in FIG. 17, a mask 1902 must be used to limit ionmilling to a selected portion of the disk while the disk is spinning.The mask 1902 can have an aperture 1904 which may be in the form of aslit or elongated opening. This aperture 1904 limits the ion beam 1702to a limited portion of the disk so that the ion milling can beperformed in a radial direction on the surface 1708 of the softunderlayer 1504.

With reference now to FIG. 20, if the ion milling is to be performed ina circumferential direction as described in FIG. 18, a mask 2002 havinga smaller aperture 2004 can be used to limit the ion beam 1702 to arelatively small portion of the surface 1708 while the disk 1602 isspinning. This aperture 2004 can be of various configurations. Howeverit should be small enough to sufficiently limit the area over which theion beam 1702 acts and should be sufficiently large to allow the ionbeam 1702 to effectively etch the surface 1708.

It should be pointed out that, while the above described process hasbeen described in terms of a surface treatment of the surface 1708 ofthe soft magnetic underlayer 1504 other treatment methods could be usedas well that fall within the scope of the invention. The treatment couldbe performed on the underlying layer on which the soft underlayer 1504is deposited. For example, the surface of the substrate 1502 (FIGS. 17,18) could be treated by ion milling as described above, and the softunderlayer 1704 could be deposited on that treated surface. The ionmilling treatment could be performed on the substrate 1502 itself, or athin layer of a desired sub-layer material could be deposited on thesubstrate 1502 and the surface of that thin sub-layer material could betreated by ion milling with the beam 1702. The soft underlayer 1502could then be deposited over the sub-layer, resulting in a radialmagnetic anisotropy in the deposited soft magnetic underlayer 1502.

In addition, since the effectiveness of the surface treatment describedabove is (after removing a given amount of material) inverselyproportional to the remaining thickness of the layer being treated, thesoft underlayer could lie deposited in steps. For example, a portion ofthe magnetically soft underlayer 1504 can be deposited, followed by anion milling with the ion beam 1702, then more of the soft underlayer1504 deposited followed by another in milling with the ion beam 1702.This process can be reiterated as many times as necessary to achieve thedesired strength of magnetic anisotropy. In addition, the softunderlayer could be deposited as a laminated structure, with many layersof soft magnetic material, each separated by a thin non-magnetic layersuch as NiCr, Cr, Rh, Ru, Ta, alumina or some other material, In thatcase, all or a portion of the deposited magnetic layers or itsunderlying layer (for example the non-magnetic lamination layers) can betreated by an ion milling with the ion beam 1702. After the softunderlayer 1504 has been deposited by any of the above describedmethods, a layer of hard magnetic material can be deposited to form thehard magnetic top layer 1506 of the disk 1602.

Magnetic Shields Having a Magnetic Anisotropy Induced by Direct IonMilling

With reference now to FIG. 21, a magnetic write head 2100 according toan embodiment of the invention as viewed from the direction of amagnetic medium (not show) (ie. as viewed from the air bearing surface(ABS)) includes a magnetoresistive sensor 2102 and first and secondmagnetic shields 2104, 2106. The sensor 2102 is sandwiched between thefirst and second shields 2104, 2106 and is embedded in a dielectriclayer 2108.

One or both (preferably both) of the magnetic shields 2104, 2106 have amagnetic anisotropy 2110 that is oriented substantially perpendicular tothe track direction and substantially parallel with the medium facingsurface or air bearing surface (ABS) of the read head 2100 as shown inFIG. 21. This magnetic anisotropy is created by one or more surfacetexture treatments that will be described in greater detail hereinbelow.

With reference now to FIGS. 22 and 23, in an embodiment of theinvention, a magnetic shield structure 2302 is constructed upon asubstrate 2304. The substrate 2304 can be a non-magnetic, electricallyinsulating gap or fill layer such as alumina (Al₂O₃) or some othermaterial. As shown in FIG. 23, the shield structure 2302 may includemultiple layers of magnetic material 2306 each of which (or a selectedportion of which) has a surface 2308 treated with an anisotropic surfacetexture. The magnetic layers 2306 can be constructed of, for exampleNiFe or some other magnetic (preferably permeable, low coercivity)material. The shield structure 2302 can be constricted by depositing amagnetic layer 2306, and performing a static angled ion milling with anion beam 2310 as shown in FIG. 22. Then, another layer of magneticmaterial 2306 is deposited and another ion milling with an ion beam 2310is performed on the surface 2308 of that layer. This process isreiterated until a complete shield having a desired magnetic anisotropy2312 has been constructed.

The treated surfaces 2308 (or interface between the magnetic layers2306) are provided with the anisotropic surface texture by the angledion milling with the ion beam 2310. This ion milling procedure and theresulting, anisotropic roughness are described in greater detail withreference to FIGS. 5A through 5D). The direction at which the ionmilling with the ion beam 2310 is performed and the orientation of theresulting anisotropic roughness depends upon the material compositionused to construct the magnetic layers 2306 as well as possibly otherfactors such as the ion beam energy or substrate temperature. However,the direction of the ion milling with the ion beam 2310 and resultingsurface texture are chosen so as to induce a magnetic anisotropy 2312 inthe magnetic layers 2306 in a direction substantially parallel with theair bearing surface (ABS) and substantially perpendicular to the writetrack direction.

With reference now to FIG. 24, in another possible embodiment of theinvention, a magnetic shield structure 2402 constructed upon a substrate2304 includes multiple layers 2406 of magnetic material separated bythin layers of non-magnetic material 2408. In this laminated shieldstructure 2402 the magnetic layers 2406 may be constructed of NiFe orsome other magnetic material. The non-magnetic lamination layers 2408may be constructed of, for example NiCr, Cr, Rh, Ru, alumina, Ta, orsome other non-magnetic material and may be electrically conductive orelectrically insulating as desired. The magnetic layers 2406 each have asurface 2412 treated with an anisotropic roughness that induces amagnetic anisotropy 2414 in the magnetic layers 2406. The anisotropically textured surfaces (or interfaces between the magnetic layers 2406and non-magnetic layers 2408) can be treated by an ion milling with anion beam 2310 oriented in such a manner as to create the desiredmagnetic anisotropy 2414 in the magnetic layers 2406. As mentionedabove, the ion milling is described in greater detail with reference toFIGS. 5A-5D. Although the ion milling is shown as being performed on thetop magnetic layer 2406, it should be understood that the ion millingcan be performed on each (or a selected number) of the magnetic layers2406 prior to depositing the subsequent non-magnetic layer 2408.

The laminated structure of the shield 2402 advantageously prevents theformation of domains in the shield 2402, and also increases theeffective anisotropy 2414 by providing an antiparallel coupling betweenthe magnetic layers 2406. The effectiveness of the milling inducedsurface treatment of a magnetic layer in creating a magnetic anisotropyin the magnetic layer (after removing a given amount of material) isinversely proportional to the remaining thickness of the magnetic layerbeing treated. Therefore, by creating multiple magnetic layers andmultiple surface treatments, the amount of magnetic anisotropy 2414 forthe magnetic shield is increased dramatically. This benefit applies tothe structure described with reference to FIG. 23 as well as theembodiment described with reference to FIG. 24.

While the embodiment described with reference to FIG. 24 has beendescribed as having the surface of each of the magnetic layers 2408treated by ion milling, it should be pointed out that in addition to orin lieu of treating the surface 2412 of the magnetic layers, the surfaceof the non-magnetic layer 2408 can be treated as well. In that case, thetreatment of the surface of the non-magnetic layer creates ananisotropic texture in the surface of the non-magnetic layer 2408 thatinduces a magnetic anisotropy in the magnetic layer 2406 deposited thereover.

With reference now to FIG. 25, another embodiment of the inventionincludes a single layer shield 2502 formed over the substrate 2304. Themagnetic shield 2502 can be constructed of a magnetic material such asNiFe or some other material and has a surface 2506 that has been treatedby an angled ion milling to provide it with an anisotropic texture. Aswith the previously described embodiments, the ion milling and resultingsurface texture are chosen to induce a magnetic anisotropy 2508 that isoriented substantially perpendicular to the track direction andsubstantially parallel with the ABS. Also as with the previouslydescribed embodiments the ion milling and resulting surface texture aredescribed in greater detail in FIGS. 5A through 5D. Also, in additionto, or in lieu of, treating the surface 2506 of the magnetic shield 2502with the ion milling, a similar ion milling can be performed on theunderlying substrate to create an anisotropic surface texture in thesubstrate 2304 that will induce a desired magnetic anisotropy in thelater deposited shield 2502.

With reference now to FIG. 26, a magnetic shield 2602 can be constructedupon an underlayer 2606 over a substrate 2304. Again the shield 2602 isconstructed of a magnetic material such as NiFe, and the substrate 2304can be alumina or some other material. The underlayer 2606 has a surface2608 (interface between the underlayer 2606 and shield 2602) that hasbeen treated by an ion beam 2310 to give it an anisotropic surfacetexture. The underlayer 2606 is constructed of a material such asNiFeCr, NiCr, Rh, Ta, Ru that is chosen to induce a strong magneticanisotropy 2610 in the magnetic shield 2602. The surface 2608 can betreated by an ion milling as described with reference to FIGS. 5Athrough 5D. In addition to treating the surface 2608 of the underlayer2606, the surface 2612 of the shield 2602 can be similarly treated by anion milling to create an anisotropic surface texture that will increasethe magnetic anisotropy 2610 in the shield 2602.

Uncontrolled domain structures in magnetic shields cause unwanted noiseand performance issues in shielded magnetic sensors. The magneticanisotropy provided by the present invention inhibits the formation ofthese undesirable domain structures in the shields, thereby increasingthe performance of the shields. The present invention provides a desiredmagnetic anisotropy without increasing the coercivity of the shield. Ithas been found that providing a magnetic anisotropy in a magneticshield, especially in the initial layers of the shield, decreases noisein the sensor. Also, creating a magnetic anisotropy in the shieldprevents the shield from becoming saturated in the pole direction(perpendicular to the medium), thereby preventing the shield fromerasing data from the magnetic media.

With reference now to FIGS. 27-29, the effect of ion milling on magneticanisotropy can be seen more clearly. FIGS. 27-29 illustrate theanisotropy energy created by milling an initially 500 Angstrom thickNiFe₁₄ film. As can be seen with reference to FIG. 27 the effect of ionmilling saturates after about 15 minutes, or after about 150 Angstromshave been removed. This further shows that after removing sufficientmagnetic material (in the case of NiFe about 150 Å) the etch inducedanisotropy behaves as a surface anisotropy since the anisotropy fieldH₁, scales with the inverse thickness of the remaining magnetic layermaterial. With reference to FIG. 29, the anisotropy energy for a givenmilling time (here 5 minutes) is constant regardless of the initialmagnetic firm thickness, except if the final film thickness becomes toothin (which is here the case if the initial NiFe₄ film thickness is 5nm).

Use of Anisotropic Etching in a Magnetic Random Access Memory (MRAM)Array

The desired characteristics of a memory system for computer main memoryare high speed, low power, non-volatility, and low cost. Low cost isaccomplished by a simple fabrication process and a small surface area.Dynamic random access memory (DRAM) cells are fast and expend littlepower, but have to be refreshed many times each second and requirecomplex structures to incorporate a capacitor in each cell. Flash typeEEPROM cells are non-volatile, have low sensing power, and can beconstructed as a single device, but take microseconds to write andmilliseconds to erase, which makes them too slow for many applications,especially for use in computer main memory. Conventional semiconductormemory cells such as DRAM, ROM, and EEPROM have current flow in theplane of the cell, i.e. “horizontal”, and therefore occupy a totalsurface area that is the sum of the essential memory cell area plus thearea for the electrical contact regions, and therefore do not achievetheir theoretical minimum cell area.

Unlike DRAM, a magnetic memory cell that stores information as anorientation of magnetization of a ferromagnetic region can hold storedinformation for long periods of time, and is thus non-volatile. Amagnetic memory cell that uses the magnetic state to alter theelectrical resistance of the materials near the ferromagnetic region canbe described as a magnetoresistive (MR) memory cell. An array ofmagnetic memory cells can be called magnetic RAM or MRAM.

Although many types of MR cells could been used in an MRAM array,magnetic tunnel junction sensors (MTJ), also called tunnel valves, arepreferable; although other magnetic memory cells such as currentperpendicular to plane giant magnetoresistive (CPP GMR) cells can beused as well.

With reference now to FIG. 30, a magnetic random access memory array3000 includes a plurality of memory cells 3002 positioned atintersections of an exemplary rectangular grid of electricallyconductive word lines 3004 and bit lines 3006. The word lines 3004 arearrayed as parallel lines in a first plane, and the bit lines 3006 arearrayed in parallel lines, perpendicular to the word lines in a secondplane. Each magnetic memory cell 3002 connects one word line 3004 with abit line 3006, bridging the space between the planes of the word linesand bit lines at the intersection of the word and bit line 3004, 3006.Although three word lines and three bit lines are shown in FIG. 2, thisis for purposes of illustration only and the actual number of word lines3004, bit lines 3006 and magnetic memory cells 3002 would be muchlarger.

During a sensing or reading operation of the array, current flows in avertical direction through the cell 3002. The vertical current paththrough the cell 3002 permits the magnetic memory cell to occupy a verysmall surface area. The array may be formed on a substrate (not shown),which contains other circuitry. The magnetic memory cell is amagneto-resistive cell that has high and low resistance states (i.e. onand off) that correlate to the magnetic state of layers within thesensor. The memory state of the sensor 3002 can be switched by,conducting a current through the word and bit lines 3004, 3006associated with a particular memory cell 3002 to thereby cause magneticfields to emanate from the particular word and bit lines 3004, 3006.This switching process will be discussed in more detail below afterfurther discussion of the structure of the cell 3002.

With reference now to FIG. 31, a magnetic memory cell 3100 according toan embodiment of the invention is sandwiched between a word line 3112and a bit line 3114. The bit line 3114 is shown in cross section in FIG.31 and would extend into and out of the plane of the page.

The memory cell includes first and second magnetic layers 3102 and 3106.A non-magnetic layer 3110 is sandwiched between the first and secondmagnetic layers 3102, 3106, and may be a non-magnetic, electricallyinsulating barrier layer (if the cell 3100 is a tunnel valve) or anon-magnetic, electrically conductive spacer layer (if the cell 3100 isa CPP GMR sensor).

The first magnetic layer 3102 has a magnetization 3116 that is pinned ina desired direction. This first magnetic layer 302 can therefore, bereferred to as a pinned layer. The printed layer can be a laminatedstructure such as an antiparallel-coupled pinned layer structure, suchas FM1/AFC/FM2, where FM1 and FM2 are two ferromagnetic layers such asCoFe or NiFe and AFC is an anti-parallel coupling layer such as Ru, Ir,Cr, or Rh. The second magnetic layer 3106 has a magnetization 3118 thatcan move between two stable states either parallel (as shown) oranti-parallel with the magnetization 3146 of the pinned layer 3102. Thissecond magnetic layer 3106 can, therefore, be referred to as a freelayer. Pinning of the magnetization 3116 of the pinned layer 3102 can bemaintained by an exchange field caused by exchange coupling of thepinned layer 3102 with a layer of antiferromagnetic material AFM layer3104.

The AFM layer 3104 can be constructed of PtMn, IrMn or some otherantiferromagnetic material. The first and second magnetic layers 3102,3106 can be constructed of a magnetic material such as CoFe, NiFe orsome combination of these or other materials. The non-magnetic layer3110 can be alumina (Al₂O₃) magnesium oxide (MgO_(x)), titanium oxide(TiO_(x)), or some other electrically insulating material (if the cell3100 is a tunnel valve) or can be an electrically conductive materialsuch as Cu (if the cell 3100 is a CPP-GMR sensor). The word and bitlines 3112, 3114 can be constructed of Cu, Au, or some otherelectrically conductive, non-magnetic material.

Alternatively to a pinned layer exchanged coupled to an AFM layer, thefirst magnetic layer 3102 may be a magnetic layer exhibiting much largercoercivity than the second magnetic layer 3106, for exampleCo_(1−x)Pt_(x) (8<x<30 at %). In that case layer 3104 may be anunderlayer such as Cr, CrV, CrTi, or CrMo.

With continued reference to FIG. 31, the cell 3100 functions based onthe spin dependent tunneling (in the case of a tunnel valve) or spindependent scattering (in the case cf a GMR sensor) of electrons throughthe non-magnetic barrier/spacer layer 3110. When the magnetizations3116, 3118 of the pinned layer 31O2 and free layer 3106 are parallel toone another (ie. in the same direction) electrical current can flowrelatively freely through the cell 3100 from between the word and bitlines 3112, 3114. In this state the cell 3100 is considered to be in the“on” state. When the magnetizations 3116, 3118 are antiparallel to oneanointer (ie. in opposite directions) the flow of current through thecell 3100 is restricted and the cell 3100 is considered to be in the“off” state.

In order to flip the magnetization of the free layer 3106 from oneorientation to another current can be caused to flow through the wordand bit lines 3112, 3114. For example, if the magnetization 3118 of thefree layer 3106 is initially oriented as shown in FIG. 31, a current3120 through the word line 3112 creates a magnetic field 3122 about theword line 3112. This magnetic field causes the magnetization 3118 of thefree layer 3106 to rotate from its initial orientation. An electricalcurrent 3124 (shown as into the page in FIG. 31) creates a magneticfield 3126 about the bit line 3114. This magnetic field 3114 completesthe switching of the magnetization 3118 of the free layer, causing themagnetization 3118 to switch (in this illustrative case) to the leftrather than to the right.

As can be appreciated, some mechanism is needed to cause themagnetization 3118 of the free layer 3106 to be stable in either the“off” or “on” state (ie. to the right or to the left), while stillallowing the magnetization 3118 to be free to rotate from one state tothe other. To meet this need, the free layer has a magnetic anisotropy3128. This magnetic anisotropy is generated, at least in large part, byan anisotropic roughness.

The free layer 3106 has a surface 3130, which can be treated by anangled, direct ion milling that produces an anisotropic surfaceroughness or texture (not shown in FIG. 31). This anisotropic surfacetexture induces a uniaxial magnetic anisotropy 3128 in the free layer3106 in a desired direction parallel with the magnetization 3116 of thepinned layer 3116. This direct angled ion milling and the resultinganisotropic surface texture or roughness is described in much greaterdetail with reference to FIGS. 5A-5D, wherein the layer 502 correspondsto the free layer 3106 in FIG. 31.

Alternatively, rather than treating the surface of the free layer 3106with the angled direct ion milling described above, the surface of theunderlying barrier/spacer layer 3110 can be treated with the angled ionmilling described in FIGS. 5A-5D. In this case, the layer 502 describedin FIGS. 5A-5D corresponds to the barrier spacer layer 3110 in FIG. 31.The resulting anisotropic surface roughness of the surface 3132 of thebarrier/spacer layer 3110 results in a desired magnetic anisotropy inthe later deposited free layer 3106.

In addition to the magnetic anisotropy 3128 of the free layer 3106 thepinned layer 3102 can be treated in a similar manner to give it amagnetic anisotropy that is also parallel with the magnetic anisotropy3128 of the free layer 3106. This can be accomplished by treating thesurface of the pinned layer 3102 as described in FIGS. 5A-5D to createan anisotropic surface texture or by treating the surface of the AFMlayer 3104 as described in FIGS. 5A-5D to create an anisotropic surfacetexture on the surface of the AFM layer 3104. If the pinned layer islaminated such as an FM1/FM2 the top surface of each FM1, AFC, FM2 canbe treated as described in FIGS. 5A-5D to create an anisotropic surfacetexture.

Alternatively, if the first magnetic layer 3102 is a hard magnetic layersuch as Co_(1−x)Pt_(x)(8<x<30 at %), the surface of the underlayer 3104can be treated as described in FIGS. 5A-5D to create an anisotropicsurface texture on the surface of the underlayer layer 3104.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example only, and notlimitation. Other embodiments falling within the scope of the inventionmay also become apparent to those skilled in the art. Thus, the breadthand scope of the invention should not be limited by any of theabove-described exemplary embodiments, but should be defined only inaccordance with the following claims and their equivalents.

1. A method for manufacturing a magnetically anisotropic magnetic layer,comprising: providing a substrate; depositing a magnetic layer over thesubstrate; depositing a sacrificial layer on the magnetic layer; andperforming an ion milling on the sacrificial layer until the magneticlayer has been exposed, the ion milling being performed at an anglerelative to a normal to a surface of the magnetic layer in order to forman anisotropic surface texture on the magnetic layer.
 2. The method asin claim 1 further comprising, while performing the ion milling,detecting removal of the sacrificial layer, and terminating the ionmilling when the sacrificial layer has been removed.
 3. The method as inclaim 1 further comprising, while performing the ion milling, using anetch detector to detect removal of the sacrificial layer, andterminating the ion milling when the sacrificial layer has been removed.4. The method as in claim 1 further comprising, while performing the ionmilling, using a secondary ion mass spectrometer to detect removal ofthe sacrificial layer, and terminating the ion milling when thesacrificial layer has been removed.
 5. The method as in claim 1 whereinthe ion milling is performed without rotation of the magnetic layerrelative to the ion beam.
 6. The method as in claim 1 wherein the ionmilling is performed at an energy of 80 to 120 eV.
 7. The method as inclaim 1 wherein the angled ion milling is performed at an angle of 25-65degrees relative to normal.
 8. The method as in claim 1 wherein theangled ion milling is performed at an angle of 20-80 degrees relative tonormal.
 9. The method as in claim 1 wherein the anisotropic surfacetexture induces a magnetic anisotropy in the magnetic layer.
 10. Themethod as in claim 1, wherein the sacrificial layer is a material thatis different from the magnetic layer.
 11. A method for manufacturing amagnetically anisotropic magnetic layer, comprising: providing asubstrate; depositing a magnetic layer over the substrate; depositing anindicator layer on the magnetic layer; depositing a sacrificial layer onthe indicator layer; and performing an ion milling on the sacrificiallayer, the ion milling being performed at an angle relative to a normalto a surface of the magnetic layer to from an anisotropic surfacetexture that induces a magnetic anisotropy in the magnetic layer. 12.The method as in claim 11 wherein the ion milling is performed until theindicator layer has been reached.
 13. The method as in claim 11 whereinthe ion milling is performed until the indicator layer has been removed.14. The method as in claim 11 wherein the anisotropic surface texture isformed in the surface of the magnetic layer.
 15. The method as in claim11 further comprising, while performing the ion milling, detecting thematerial removal to determine when the indicator layer has been reached.16. The method as in claim 11 further comprising, while performing theion milling, using an etch detector to determine when the indicatorlayer has been reached.
 17. The method as in claim 11 furthercomprising, while performing the ion milling, using a secondary ion massspectrometer to determine when the indicator layer has been reached. 18.The method as in claim 11 wherein the indicator layer comprises amaterial selected from the group consisting of Ta Ru Pt, Cr, Pd, Ti andAl.
 19. The method as in claim 11 wherein the sacrificial layercomprises a material selected from the group consisting of Ru, Ta, Au,Cu and Ag.
 20. The method as in claim 11 wherein the ion milling isperformed at an energy of 80 to 120 eV.
 21. The method as in claim 11wherein the angled ion milling is performed at an angle of 25-65 degreesrelative to normal.
 22. The method as in claim 11 wherein the angled ionmilling is performed at an angle of 20-80 degrees relative to normal.23. The method as in claim 11 wherein the ion milling is performedwithout rotating the magnetic layer.
 24. The method as in claim 11wherein the indicator layer is a material that is more resistant to ionmilling than the sacrificial layer and wherein the indicator layer actsas a milling stop.